Oral care compositions, such as toothpastes, may comprise zinc complexes as active ingredients. Zinc (II) ions are useful in the treatment of various diseases and disorders of the oral cavity. For example, zinc (II) has been used in the treatment of halitosis and as an antiplaque agent.
It has been reported previously that only free zinc (II) ions display these useful effects (U.S. Pat. No. 4,992,259). Oral care compositions are generally complex mixtures of multiple ingredients. Certain ingredients may interact with zinc and limit its availability. In most cases, the ability of a composition to release zinc (II) is not readily predictable and must be determined empirically.
Various methods for measuring the amount of zinc delivered by a composition have been proposed.
Atomic absorption spectroscopy (AAS) is useful for the quantitative determination of various elements, and has been used to measure the amount of zinc present in saliva following toothbrushing (Ozedimir et al, 1998. “The Determination of Salivary Zinc Level Following Delivery from Zinc Containing. Toothpaste”, Tr. J. of Medical Sciences, 28. pp 281-283).
The use of a zinc composition enriched with a stable zinc isotope (68Zn) with detection by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has been applied to the analysis of the absorption of zinc oxide particles from sunscreens by human skin (Gulson et al. 2010. “Small amounts of zinc from zinc oxide particles in sunscreens applied outdoors are absorbed through human skin” Toxicological Sciences, 118, 1, pp 140-149). The unstable zinc isotope 65Zn has also been used to investigate the percutaneous absorbtion of zinc in the guinea pig (Skog and Wahlberg, 1964. “A comparative investigation of the percutaneous absorption of metal compounds in the guinea pig by means of radioactive isotopes: 51Cr, 58Co, 65Zn, 110mAg, 115mCd, 203Hg”, J Invest Dermatol, 43, 3, pp 187-192).
Although these methods allow the quantitation of absorbed zinc, they do not discriminate between therapeutically-active zinc (II) ions and inactive bound zinc. Furthermore, relatively complex apparatus is required. There remains a need in the art for a rapid and simple method for estimating the therapeutically-active zinc delivered by an oral care composition.